Touch panel displays can be implemented using a variety of underlying technologies to provide touch input. The underlying technologies include, for example, resistive touch input systems, capacitive touch input systems, acoustic wave touch input systems, and infrared touch input systems. There are also other technologies used to implement touch input systems, such as near field imaging and corner camera imaging.
For miniature devices such as personal digital assistants (PDAs) and hand phones, the most common technologies used for touch input systems are resistive touch input systems and capacitive touch input systems.
Infrared touch input systems have been used in many applications such as, for example, automated teller machines (ATMs), food service and preparation computers, KIOSKs, medical instrumentation, process control systems, and transportation tracking applications. One advantage of infrared touch input systems is that these systems do not require that any material that could inhibit screen clarity or brightness be placed over a display screen.
Infrared touch input systems typically use light-emitting diodes (LEDs) along with opposing photodiodes or phototransistor detectors that operate above a display surface. A special bezel is used over the LEDs and photodiodes or phototransistors above the display surface. Controller circuitry controls scanning above the display surface with an invisible lattice of infrared light beams. The scanning is implemented by LEDs generating pulsed light beams that are detected by opposing photodetectors. Failure to detect light beams of a pulsed LED indicates an object, such as a stylus or finger, has interrupted the light beam transmission.
The space required to house LEDs and photodetectors can undesirably increase the size necessary to implement an infrared touch input system for miniature devices such as hand phones and PDAs. The LEDs and photodetectors are typically mounted on rectangular frame and extend the length and width of the device. It is important, therefore, to minimize the form factor for infrared optical touch input devices used for miniature devices such as hand phones and PDAs.